System for monitoring physiological characteristics

ABSTRACT

Apparatuses and methods for medical monitoring physiological characteristics values such as blood glucose levels for the treatment of diabetes, are presented. The apparatuses and methods provide dynamic glucose monitoring functions that perform predictive analysis to anticipate harmful conditions, such as glucose crash and hyperglycemic incidents for a patient. The dynamic functions can also be used to maximize athletic performance and warn of inadequate nocturnal basal rate. Other aspects include advanced alarm and reminder functions, as well as advanced data presentation tools to further facilitate convenient and efficient management of various physiological conditions.

This application is a divisional application of U.S. patent applicationSer. No. 10/034,139, filed Dec. 27, 2001, by James Kelley Fox et al, andentitled “SYSTEM FOR MONITORING PHYSIOLOGICAL CHARACTERISTICS”, thecontents of all of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to medical monitoring systems. Morespecifically, this invention relates to methods and systems formonitoring physiological characteristics in individuals including thoseassociated with physiological conditions (e.g. monitoring blood glucoselevels in diabetics).

2. Description of the Related Art

A variety of electrochemical sensors have been developed for detectingand/or quantifying specific agents or compositions in a patient's blood.Notably, glucose sensors have been developed for use in obtaining anindication of blood glucose levels in a diabetic patient. Such readingsare useful in monitoring and/or adjusting a treatment program whichtypically includes the regular administration of insulin to the patient.Periodic blood glucose readings significantly improve medical therapiesusing semi-automated medication infusion devices. Some exemplaryexternal infusion devices are described in U.S. Pat. Nos. 4,562,751,4,678,408 and 4,685,903, while some examples of automated implantablemedication infusion devices are described in U.S. Pat. No. 4,573,994,all of which are herein incorporated by reference.

Electrochemical sensors can be used to obtain periodic measurements overan extended period of time. Such sensors can include a plurality ofexposed electrodes at one end for subcutaneous placement in contact witha user's interstitial fluid, blood, or the like. A correspondingplurality of conductive contacts can be exposed at another end forconvenient external electrical connection with a suitable monitoringdevice through a wire or cable. Exemplary sensors are described in U.S.Pat. No. 5,299,571, U.S. Pat. Nos. 5,390,671; 5,391,250; 5,482,473; and5,586,553, which are all incorporated by reference herein.

Conventional glucose monitoring systems are somewhat limited in featuresthat they provide to facilitate the monitoring of blood glucose levels.Typically, a glucose monitor will take readings as directed by the userand might provide a warning if a reading is deemed at an unsafe level(e.g., a hyper- or hypoglycemic condition). However, by the time thewarning occurs, the user may already be experiencing negative symptoms.Furthermore, it may be unacceptable to address this by simply reducing(or raising) the value which triggers an indicator (e.g. an display, analarm or the like) of an unsafe condition, because this may prompt auser to take “remedial” action (such as administering an additionalbolus) when no unsafe condition would have actually materialized. Suchan approach merely increases the occurrence of false positive alarms. Asa consequence, the unnecessary “remedial” action can actually provoke anunsafe condition. As described above, although existing glucose monitorsadequately detect blood glucose levels upon entering the hyperglycemicrange, they do not anticipate these conditions.

As is known in the art, a glucose crash occurs when blood glucose levelsof an individual are in a state of rapid decline and its symptoms aresimilar to those associated with hypoglycemia. The symptoms are causedby the dynamics of a declining glucose level and not by an absoluteglucose level. Specific symptoms can include a feeling of lightheadedness, sweating, tremors, nervousness and/or disorientation.Disorientation is a particular risk to the patient. If the patientbecomes disoriented while operating machinery, the patient could harmhimself or others. A glucose crash can be caused by any of the followingevents: excess insulin administration; an unexpected increase in insulinsensitivity; a fall of free fatty acids in the blood; heavy exercise; ormental or physical stress. As previously mentioned, ordinary glucosemonitors provide only for detection of hypoglycemic and hyperglycemiclevels.

Impaired fasting glucose (IFG) is another condition which is notpredicted by conventional glucose monitors. The American DiabetesAssociation (ADA) identifies IFG as an undesirable glucose condition,defined as a 126 mg/dL or higher blood glucose level at wakeup. RepeatedIFG events can contribute to diabetic morbidity. One cause of IFG is aninadequate nocturnal insulin basal infusion rate. Although a patient candeal with the IFG after waking by administering an insulin bolus, it ispreferable for the patient to avoid IFG incidents entirely.

Typical monitors provide only a single alarm to call attention to theuser. This can be problematical in contexts of varying physiologicalstates because a user is not made aware of the specific condition and/orthe appropriate degree of urgency. In existing alarm systems, until theuser investigates, there is no indication of the reason for the alarm orthe severity of the situation.

Conventional monitors are designed to alert the user of unsafeconditions, however, many other factors and situations are alsoimportant to the user in managing treatment. For example, events such asmeals or exercise, as well as entering calibration values are not tiedto reminders issued by conventional monitors. In addition, simple alarmsystems alarms can provide duplicative warnings which can frustrateusers and become ignored if they are excessive.

SUMMARY OF THE INVENTION

The invention as embodied and disclosed herein pertains to apparatusesand methods for monitoring physiological characteristics such as bloodglucose levels. Embodiments of the invention include dynamic monitoringfunctions that can perform predictive analyses to anticipate harmfulconditions, such as hyperglycemic (or hyperglycemic) incidents, beforethey occur. These dynamic functions can be used to monitor normalphysiological functions, as well as in a variety of other contextsincluding the optimization of athletic performance. Other embodiments ofthe invention include advanced alarm and reminder functions, as well asadvanced data presentation tools. Embodiments of the invention disclosedherein facilitate the convenient and efficient management of diseasessuch as diabetes.

One embodiment of the invention includes a method of monitoring aphysiological characteristic of a user using a device including an inputelement capable of receiving a signal from a sensor that is based on asensed physiological characteristic value of the user, and a processorfor analyzing the received signal. In typical embodiments of theinvention, the processor determines a dynamic behavior of thephysiological characteristic value and provides an observable indicatorbased upon the dynamic behavior of the physiological characteristicvalue so determined. In a preferred embodiment, the physiologicalcharacteristic value is a measure of the concentration of blood glucosein the user. In another embodiment, the process of analyzing thereceived signal and determining a dynamic behavior includes repeatedlymeasuring the physiological characteristic value to obtain a series ofphysiological characteristic values to determine how the physiologicalcharacteristic is changing over time.

In some embodiments of the invention, each of the series ofphysiological characteristic values includes a smoothing filtered groupof repeated physiological characteristic value readings. In suchembodiments, a slope of a line fit to the series of physiologicalcharacteristic values can be calculated if a most recent of the seriesof physiological characteristic values is within a qualifying range. Insome embodiments of the invention, the physiological characteristicvalue readings may be decreasing and the slope is negative. Typically,the indicator can also include a warning alarm that is responsive to thedynamic behavior profile of the physiological characteristic value. Thewarning alarm can also announce an anticipated glucose crash or merelylow glucose levels, depending on the operating parameters of theparticular dynamic analysis, including comparison of the slope to athreshold rate (e.g., 1% to 3% per minute) and comparison of the currentmeasured value to a qualifying range (e.g., 60 to 150 mg/dL). In typicalembodiments, the series of values analyzed is taken from a defined spanof time (e.g., ten to thirty minutes).

In other typical embodiments of the invention, an anticipatedphysiological characteristic value is determined from an extrapolatedcurve based upon the series of physiological characteristic values. Insuch embodiments the indicator can provide a warning of an anticipatedmorning glucose incident. In preferred embodiments, the series of valuesanalyzed can also be taken from a defined span of time (e.g. one hour).In one embodiments, the extrapolated curve is determined from a slope ofa line fit to the series of physiological characteristic values and anaverage of the series of physiological characteristic values. In anotherillustrative embodiment, the anticipated physiological characteristicvalue can be determined approximately three hours before an anticipatedwakeup time. In addition, in certain embodiments, the indicator can beprovided if the anticipated value is outside a qualifying range (e.g.,approximately 60 mg/dL to 126 mg/dL).

In related embodiments of the invention, a slope of a line fit to theseries of physiological characteristic values is calculated if a mostrecent of the series of physiological characteristic values exceeds athreshold value and the slope is positive. In such embodiments, theindicator can provide a warning of an anticipated hyperglycemicincident. In an illustrative embodiment, the series of physiologicalcharacteristic values spans a time period of approximately thirtyminutes and the indicator will be provided if the slope is steeper thana threshold rate. In this context a typical threshold rate can beapproximately 3% per minute and the threshold value can be approximately180 mg/dL. In such other embodiments, the indicator can provide awarning of an anticipated hypoglycemic incident. In an illustrativeembodiment, the series of physiological characteristic values spans atime period of approximately thirty minutes and the indicator will beprovided if the slope is steeper than a threshold rate. In this contexta typical threshold rate can be approximately 3% per minute and thethreshold value can be approximately 70 mg/dL.

Another embodiment of the invention includes a physiologicalcharacteristic monitor (and corresponding methods for its use) includingan input device capable of receiving a signal from a sensor and aprocessor capable of analyzing the received signal and providingmultiple alarms, each of which can be based upon different conditionsassociated with the physiological characteristic value of the user. Inpreferred embodiments, the signal is based on a physiologicalcharacteristic value of a user. In some embodiments, the multiple alarmsare distinguishable from each other and can include any one of a widevariety of signals such as audible signals, visual signals, tactilesignals, displays, and/or the like.

In some embodiments of the invention, the processor determines aphysiological characteristic value from the received signal and themultiple alarms are based upon that value. In such embodiments, each ofthe multiple alarms can then be triggered if the physiologicalcharacteristic value exceeds an associated threshold value.

In other embodiments of the invention, one of a first pair of themultiple alarms can be triggered when a narrow range of physiologicalcharacteristic values is exceeded. The first pair of the multiple alarmsis typically associated with a first upper threshold value and a firstlower threshold value, respectively. In further embodiments, a secondpair of multiple alarms can be triggered by events a wide range ofphysiological characteristic values (e.g. exceeding a predeterminedvalue). The second pair of the multiple alarms can be associated with asecond upper threshold value and a second lower threshold value,respectively.

In yet another embodiment of the invention, a physiologicalcharacteristic monitoring method and device are disclosed which includean input device capable of receiving a signal from a sensor and aprocessor for analyzing the received signal. Typically, the signal isbased on a physiological characteristic value of a user. In preferredembodiments, the processor initiates a timer based upon a conditionassociated with the physiological characteristic value of the user andprovides a reminder to the user following expiration of the timer. Insome embodiments of the invention, the reminder can include an alarmsignal selected from the group consisting of an audible signal, a visualsignal, a tactile signal, a display, and/or the like. Typically, theduration of the timer is preset based upon the specific initiatingcondition.

In preferred embodiments of the invention, conditions which trigger theone or more alarms can vary. For example, the conditions which triggerthe one or more alarms can be an event marker such as meal markers,exercise markers, high blood glucose markers and low blood glucosemarkers. The condition(s) which trigger the one or more alarms canfurther be a reference value that is entered into the monitor and thereminder can indicate that a new reference value should be entered.

In other embodiments of the invention, the processor can determine aphysiological characteristic value from the received signal and thetriggering condition is then based upon that physiologicalcharacteristic value. For example, the triggering condition can besituations where the physiological characteristic value exceeds apredetermined threshold value.

Other embodiments of the invention include a physiologicalcharacteristic monitor including an input device capable of receiving asignal from a sensor, a processor for analyzing the received signal anddetermining physiological characteristic value data of the user from thereceived signal, a memory for storing the physiological characteristicvalue data of the user and a display. Typically, the signal is based ona physiological characteristic value of a user. In preferredembodiments, the display provides a retrospective display of thephysiological characteristic value data. In some embodiments of theinvention, the stored physiological characteristic value data includes aminimum and maximum blood glucose value and the retrospective displayshows the minimum and maximum blood glucose value with a respective timeand date. In other embodiments, the stored physiological characteristicvalue data can include a first number of excursions above an upper bloodglucose value and a second number of excursions below a lower bloodglucose value and the retrospective display shows the first and secondnumber.

In other embodiments of the invention, the stored physiologicalcharacteristic value data can include a distribution of blood glucosevalues and the retrospective display shows a first portion of the bloodglucose values above an upper blood glucose value, a second portion ofthe blood glucose values below a lower blood glucose value and a thirdportion of the blood glucose values between the upper value and thelower value. In preferred embodiments, the portions can be shown aspercentages, times or numbers of readings. The display can include atotal time for the physiological characteristic value data as well asthe total number of readings for the physiological characteristic valuedata. In preferred embodiments of the invention, the first portion andthe second portion can be shown as integrated values. The integratedvalues can be based on the sums of magnitude differences from the upperblood glucose value and the lower blood glucose value for the first andsecond portion, respectively. In such embodiments, the integrated valuescan be divided by a respective duration of sensor use.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1 is a block diagram of a characteristic monitor embodiment of thepresent invention.

FIG. 2 is a block diagram of a telemetered characteristic monitorembodiment of the present invention;

FIG. 3A is a flowchart of a method for anticipating a glucose crash;

FIG. 3B is a flowchart of a method for detecting an inadequate nocturnalbasal rate;

FIG. 3C is a flowchart of a method for anticipating a hyperglycemicincident;

FIG. 3D is a flowchart of a method for maximizing athletic performance;

FIG. 4 illustrates a multiple alarm function of the invention;

FIG. 5 illustrates a reminder function of the invention;

FIG. 6A illustrates minimum and maximum data presentation;

FIG. 6B illustrates excursion data presentation;

FIG. 6C illustrates characteristic value distribution data presentation;and

FIG. 6D illustrates integrated characteristic value data presentation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 1. Overview

Embodiments of the present invention encompass methods and systems forthe convenient operation of monitoring physiological characteristics(“characteristic monitoring systems”). The description provided hereencompasses the architecture of the apparatus as well as its control andconvenience features. The control and convenience features of thepresent invention can be implemented in a wide range of detailedcharacteristic monitoring system designs. Although embodiments of thepresent invention are primarily described in the context of glucosemonitors used in the treatment of diabetes, the embodiments of theinvention are applicable to a wide variety of patient treatment programswhere a physiological characteristic is periodically monitored to use inestimating the responsive treatment. For example, embodiments of theinvention can be used to determine the status and/or levels of a varietyof characteristics including those associated with agents such ashormones, cholesterol, medication concentrations, pH, oxygen saturation,viral loads (e.g., HIV), or the like As is known in the art, a sensorfor the characteristic monitor can be implanted in and/or throughsubcutaneous, dermal, sub-dermal, inter-peritoneal or peritoneal tissue.Such sensors typically communicate a signal from the sensor set to thecharacteristic monitor.

General embodiments of the invention include a physiologicalcharacteristic monitor coupled to a sensor set. In preferredembodiments, the sensor set and monitor are for determining glucoselevels in the blood and/or body fluids of the user without the use of,or necessity of, a wire or cable connection between the transmitter andthe monitor.

Embodiments of the characteristic monitor system of the invention areprimarily adapted for use in subcutaneous human tissue. Alternatively,embodiments of the invention can be placed in a variety of other typesof physiological milieus, such as muscle, lymph, organ tissue, veins,arteries or the like, as well as being used in related environments suchas animal tissue. Embodiments of the invention can provide sensorreadings on an intermittent, near-continuous or continuous basis.

Embodiments of the invention include sensing and advanced predictivefunctions of the monitor which are designed to anticipate unsafeconditions for a user before they occur. In addition, predictivefunctions can be employed so that a user can obtain feedback to obtain adesired physical objective, such as maximizing athletic performance.Other functions of the monitor include multiple programmable alarms andreminders. Embodiments of the invention can include advanced displaytools to facilitate easy and quick interpretation of information relatedto the user's condition.

2. Glucose Monitor

FIG. 1 is a block diagram of a characteristic monitoring system 100 inaccordance with an embodiment of the present invention. Thecharacteristic monitoring system 100 generally includes a sensor set 102that employs a sensor that produces a signal that corresponds to ameasured characteristic of the user, such as a blood glucose level. Thesensor set 102 communicates these signals to a characteristic monitor104 that is designed to interpret these signals to produce acharacteristic reading or value for the user, i.e. a measurement of thecharacteristic. The sensor signals enter the monitor 104 through asensor input 106 and through the sensor input 106 the signals areconveyed to a processor 108. The processor 108 determines andmanipulates the sensor readings within the monitor 104. In addition, butnot limited to, the characteristic monitor 104 provides additionalfunctions that will aid in the treatment regime to which thecharacteristic reading applies. For example, but not limited to, themonitor may track meals, exercise and other activities which affect thetreatment of diabetes. These additional functions can be combined withor independent from the characteristic readings determined by themonitor 104.

Other components of the monitor 104 support the processor 108 inperforming functions. A memory 110 is used to store data andinstructions used by the processor 108. A data entry device 112 such asa keypad is used to receive direct input from the user and a display 114such as a liquid crystal display (LCD), or the like, is used to relateinformation to the user. In addition, the monitor 104 includes a dataport 116, such as a digital input/output (I/O) port.

The data port 116 can be used for the monitor to communicate with acomputer 118. To facilitate communication, the monitor may interfacewith the computer 118 through a communication station 120 that can serveas a docking station for the monitor 104, for example. In someembodiments, the data port 116 within the monitor 104 can be directlyconnected to the computer 118. Through the communication link, data maybe downloaded from the monitor, such as stored characteristic readings,settings, programs and other information related to the monitor'sfunction. Thus, advanced analysis can be performed on a computer freeingmemory 110 within the monitor 104. Data such as characteristic readings,settings and programs can also be downloaded to the monitor 104. In thisway, the monitor 104 can be conveniently reprogrammed without requiringtedious manual entry by the user.

FIG. 2 is a block diagram of a telemetered characteristic monitoringsystem embodiment of the invention. In this system embodiment 200, thesensor input 106 of the monitor 104 is a wireless receiver, such as aradio frequency (RF) receiver. The sensor set 102 provides a signal viawired link to a telemetered monitor transmitter 202 where the signal isinterpreted and converted to an RF signal. The wireless receiver sensorinput 106 of the monitor 104 converts the signal to data understandableto the monitor processor. With some advantages, the telemeteredcharacteristic monitoring system can perform any or all the functions ofthe characteristic monitoring system of FIG. 1.

A characteristic monitor system 100, in accordance with a preferredembodiment of the present invention includes a sensor set 102, andcharacteristic monitor device 104. The sensor set 102 generally utilizesan electrode-type sensor. However, in alternative embodiments, thesystem can use other types of sensors, such as electrically basedsensors, chemically based sensors, optically based sensors, or the like.In further alternative embodiments, the sensors can be of a type that isused on the external surface of the skin or placed below the skin layerof the user. Preferred embodiments of a surface mounted sensor utilizeinterstitial fluid harvested from underneath the skin. The sensor set102 is connected to the monitor device 104 and provides a signal basedupon the monitored characteristic (e.g., blood glucose). Thecharacteristic monitor device 104 utilizes the received signal todetermine the characteristic reading or value (e.g., a blood glucoselevel). In still other embodiments, the sensor may be placed in otherparts of the body, such as, but not limited to, subcutaneous, dermal,sub-dermal, inter-peritoneal or peritoneal tissue

The telemetered characteristic monitor transmitter 202 generallyincludes the capability to transmit data. In alternative embodiments,the telemetered characteristic monitor transmitter 202 can include areceiver, or the like, to facilitate two-way communication between thesensor set 102 and the characteristic monitor 104. In alternativeembodiments, the characteristic monitor 104 can be replaced with a datareceiver, storage and/or transmitting device for later processing of thetransmitted data or programming of the telemetered characteristicmonitor transmitter 202. In addition, a relay or repeater (not shown)can be used with a telemetered characteristic monitor transmitter 202and a characteristic monitor 104 to increase the distance that thetelemetered characteristic monitor transmitter 202 can be used with thecharacteristic monitor 104. For example, the relay can be used toprovide information to parents of children using the telemeteredcharacteristic monitor transmitter 202 and the sensor set 102 from adistance. The information can be used when children are in another roomduring sleep or doing activities in a location remote from the parents.In further embodiments, the relay can include the capability to sound analarm. In addition, the relay can be capable of providing telemeteredcharacteristic monitor transmitter 202 data from the sensor set 102, aswell as other data, to a remotely located individual via a modemconnected to the relay for display on a monitor, pager or the like. Thedata can also be downloaded through the communication station 120 to aremotely located computer 118 such as a PC, lap top, or the like, overcommunication lines, by modem or wireless connection. As disclosedherein, some embodiments of the invention can omit the communicationstation 120 and use a direct modem or wireless connection to thecomputer 118. In further embodiments, the telemetered characteristicmonitor transmitter 202 transmits to an RF programmer, which acts as arelay, or shuttle, for data transmission between the sensor set 102 anda PC, laptop, communication station 118, a data processor, or the like.In further alternatives, the telemetered characteristic monitortransmitter 202 can transmit an alarm to a remotely located device, suchas a communication station 118, modem or the like to summon help.

In addition, further embodiments can include the capability forsimultaneous monitoring of multiple sensors and/or include a sensor formultiple measurements.

A purpose of the characteristic monitor system 100 is to provide forbetter treatment and control in an outpatient or a home use environment.For example, the monitor systems 100, 200 can provide indications ofglucose levels, a hypoglycemia/hyperglycemia alert and outpatientdiagnostics. Embodiments of the invention are also useful as anevaluation tool under a physician's supervision.

The characteristic monitor device 104 receives characteristicinformation, such as glucose data or the like, from the sensor set 102and displays and logs the received glucose readings. Logged data can bedownloaded from the characteristic monitor 104 to a personal computer,laptop, or the like, for detailed data analysis. In further embodiments,the characteristic monitor system 100, 200 can be used in a hospitalenvironment, or the like. Still further embodiments of the presentinvention can include one or more buttons to record data and events forlater analysis, correlation, or the like. Further buttons can include asensor on/off button to conserve power and to assist in initializing thesensor set 102. The characteristic monitor 200 can also be employed withother medical devices to combine other patient data through a commondata network system.

Further embodiments of the sensor set 102 can monitor the temperature ofthe sensor set 102, which can then be used to improve the calibration ofthe sensor. For example, for a glucose sensor, the enzyme reactionactivity may have a known temperature coefficient. The relationshipbetween temperature and enzyme activity can be used to adjust the sensorvalues to more accurately reflect the actual characteristic levels. Inaddition to temperature measurements, the oxygen saturation level can bedetermined by measuring signals from the various electrodes of thesensor set 102. Once obtained, the oxygen saturation level can be usedin calibration of the sensor set 102 due to changes in the oxygensaturation levels, and its effects on the chemical reactions in thesensor set 102. For example, as the oxygen level goes lower the sensorsensitivity can be lowered. The oxygen level can be utilized incalibration of the sensor set 102 by adjusting for the changing oxygensaturation. In alternative embodiments, temperature measurements can beused in conjunction with other readings to determine the required sensorcalibration.

In preferred embodiments, the sensor set 102 facilitates accurateplacement of a flexible thin film electrochemical sensor of the typeused for monitoring specific blood parameters representative of a user'scondition. Preferably, the sensor monitors glucose levels in the body,and can be used in conjunction with automated or semi-automatedmedication infusion devices of the external or implantable type asdescribed in U.S. Pat. Nos. 4,562,751; 4,678,408; 4,685,903 or 4,573,994(which are incorporated herein by reference), to control delivery ofinsulin to a diabetic patient.

Embodiments of the flexible electrochemical sensor can be constructed inaccordance with thin film mask techniques to include elongated thin filmconductors embedded or encased between layers of a selected insulativematerial such as polyimide film or sheet, and membranes. The sensorelectrodes at a tip end of the sensing portion are exposed through oneof the insulative layers for direct contact with patient blood or otherbody fluids, when the sensing portion (or active portion) of the sensoris subcutaneously placed at an insertion site. The sensing portion isjoined to a connection portion that terminates in conductive contactpads, or the like, which are also exposed through one of the insulativelayers. In alternative embodiments, other types of implantable sensors,such as chemical based, optical based, or the like, can be used. Furtherdescription of flexible thin film sensors of this general type are befound in U.S. Pat. No. 5,391,250, entitled “METHOD OF FABRICATING THINFILM SENSORS”, which is herein incorporated by reference. The connectionportion can be conveniently connected electrically to the monitor 104 ora telemetered characteristic monitor transmitter 202 by a connectorblock (or the like) as shown and described in U.S. Pat. No. 5,482,473,entitled “FLEX CIRCUIT CONNECTOR”, which is also herein incorporated byreference. Thus, in accordance with embodiments of the presentinvention, subcutaneous sensor sets 102 are configured or formed to workwith either a wired or a wireless characteristic monitor system 100,200.

3. Dynamic Glucose Monitoring Functions

Embodiments of the present invention include different types ofcontinuous glucose monitors that identify trends in blood glucosedynamics to facilitate enhanced treatment of diabetes. In general, afirst illustrative monitor can be used to anticipate a glucose “crash”(or other hypoglycemic incident) before the onset of debilitatingsymptoms. Another illustrative monitor can be used to detect aninadequate nocturnal basal rate and alert the patient in order to avoidan impaired fasting glucose incident. Another illustrative monitor cananticipate hyperglycemic (or hypoglycemic) incidents by detecting trendstoward those levels and help the patient avoid such incidents. Anotherillustrative monitor can assist a patient in maximizing athleticperformance in endurance type activities (e.g., a marathon race) bydetecting trends toward hypoglycemic levels.

The disclosed embodiments monitor the dynamics of a physiologicalcharacteristic such as blood glucose levels. These embodiments utilizethis dynamic monitoring to provide functionality including theanticipation of glucose crash and alerting the patient, the detection ofinadequate nocturnal basal rate, the anticipation of hyperglycemic (orhypoglycemic) incidents and maximizing athletic performance. All ofthese features can be implemented in software operating in the monitor'smicroprocessor and/or designed into an application specific integratedcircuit (ASIC) or other specialized circuitry. Also, dynamic glucosemonitoring functions use periodic measurements of a glucose level.

A. Monitor for Anticipating a Glucose Crash

In one embodiment of the invention, a monitor anticipates a glucosecrash by monitoring trends in glucose levels. For example, the monitorcan alert the patient when glucose levels are rapidly decreasing. Bymonitoring such trends or a rate information of measured glucose levels,the monitor can provide a much better warning system to alert the userwith enough time to stabilize and reverse a dangerous physiologicalcondition.

In some embodiments of the invention, the monitor measures glucose morefrequently than typical glucose monitoring devices. For example, oneembodiment of the invention measures approximately every minute, whereasother monitors measure a lower rate (e.g., but not limited to, once per5 minutes). Frequent measurements are taken because of the short timeintervals which are evaluated. Alternative embodiments may utilize morefrequent measurements, such as, but not limited to, 10 seconds, 1second, or the like.

In an illustrative embodiment, the monitor periodically measuresglucose, analyzes the present trend, determines whether a glucose crashincident is probable and appropriately alerts the patient. At somefrequent interval (e.g., but not limited to, once per minute), thedevice measures the glucose level, applies a smoothing filter to theresult, and records the filtered value. The smoothing filter may take aweighted sum of past sensor values (so called finite impulseresponse—FIR-filter), a weighted sum of past sensor values and pastfiltered values (so called infinite impulse response—IIR-filters), mayuse simple clipping algorithms (e.g. limit the percent change infiltered output), or employ models to predict the output (e.g. Weinerand Kalman filter designs). For example, if the most recent (filtered)value is in the “qualifying range”, the monitor can calculate the slopeof a line fit to the most recent values (most likely, but not limitedto, using a Saritzky gulag filter) and determine if the slope is steeperthan a selected threshold rate (e.g., but not limited to, 3% ordeclining at more than 30 mg/dL in ten minutes). If the slope equals orexceeds the threshold rate, a glucose crash incident is likely and themonitor alerts the patient accordingly.

Those skilled in the art will understand that in some embodiments thequalifying range can be a closed range (e.g., but not limited to,between 100 and 150 mg/dL) and in other embodiments the qualifying rangecan be an open range (e.g., but not limited to, greater than 100 mg/dL).By first identifying whether a most recent value is within thequalifying range, further calculation of the dynamic behavior of thephysiologic characteristic can be avoided. Thus, the determination of aglucose crash can be unconcerned with rate magnitudes occurring when thecurrent characteristic value is outside of the range, (of course, otheralarms, which merely monitor the current characteristic value, can betriggered when the reading is too high or too low). However, inalternate embodiments, the slope can be calculated and compared to thethreshold rate with every new value. In further embodiments, multiplequalifying ranges and threshold rates can be applied to evaluate theglucose dynamics and determine triggering a glucose crash warning.

In one preferred embodiment, the monitor determines that a glucose crashis likely if three criteria are met. The criteria are as follows. Thefirst, dG/dT (the rate of glucose level change) is negative, can beconsidered for example in situations where blood glucose levels aredropping (e.g., but not limited to, when a value pertaining to the rateof glucose change is negative). The second, |dG/dT| exceeds a thresholdrate, can be considered in contexts, for example where a specified bloodglucose change rate is exceeded for a specified sustained period (e.g.,but not limited to, greater than 3% per minute for 10 minutes). Thethird, G, the glucose level, can be considered for example, when thisvalue begins dropping starting within a specified range, (e.g., but notlimited to, 100-150 mg/dL).

In some embodiments, these criteria can be parameterized to allow theuser to customize the values. The qualifying range, threshold rate andperiod can be general values, applied to all users, or determined fromfactors specific to the individual user. For example, the monitor caninclude a feature to adjust the qualifying glucose level range, themaximum rate of glucose change, or in some embodiments, the sustainedtime period length. In addition, in some embodiments, any or all of thedynamic glucose monitoring functions can enabled or disabled,selectively or together.

The following control program pseudo code provides an example of aprogramming routine performed by the processor of the monitor toimplement an embodiment of the invention.

REPEAT every minute) { Measure glucose level  g_(i) Filter g_(i) andstore the filtered value g′_(i) IF(g′_(i) is in range 100-150 mg/dL)THEN Fit a line to the most recent 10 filtered (or, alternatively,unfiltered) values IF (dG/dT for that line < ( −3% per minute ) THENAlert the patient and record in history ENDIF ENDIF } END REPEAT

FIG. 3A is a flowchart of a method for anticipating a glucose crash 300.At block 302, a characteristic level is repeatedly measured to obtain agroup of characteristic level values. Following this at block 304, asmoothing filter can be applied to the group of characteristic levelvalues to produce a filtered measurement value. The filtered measurementvalue is recorded at block 306. At block 308 it is determined if therecorded value falls within a qualifying range (e.g., but not limitedto, between 100 to 150 mg/dL). If not, the process returns to block 302.If the recorded measurement is within the range, a slope of a line fitto a recent series of recorded filtered values is calculated at block310. The calculated slope is compared to a threshold rate (e.g., but notlimited to, −3% per minute) at block 312. If the calculated slope is notsteeper than the threshold rate the process returns to block 302. If theslope exceeds the threshold rate, an anticipated glucose crash isindicated at block 314. Alternative embodiments may utilize similarlogic for when the glucose level is already outside of the range andcontinues to drop. In addition in an alternative preferred embodiment ofthe invention, one can utilize a raw data measurement (e.g. a group ofcharacteristic level values) to determine a derivative as an alternativeto using a filtered measurement value to determine a derivative.

B. Monitor for Detecting an Inadequate Nocturnal Basal Rate

In another embodiment of the invention, the characteristic monitor canbe used to detect an inadequate nocturnal basal rate. This embodimentgenerally applies to diabetic patients using an insulin infusion devicethat continually administers insulin at a patient controlled basal rate.The monitor detects an inadequate basal rate (i.e., but not limited to,“low basal rate” or a “high basal rate”), by monitoring trends inglucose levels. The monitor then alerts a patient in the early morning,when glucose levels are high and relatively steady, low and relativelystable or changing rapidly. This gives the patient time to adjust thebasal rate of the infusion device upward or downward to and avoid animpaired fasting glucose incident.

The monitor operates to track the characteristic level rate. Forexample, every 5 minutes the monitor measures and records the glucoselevel. Once a day (e.g., but not limited to, 3 hours before to theanticipated wakeup time), the monitor calculates the average bloodglucose and the rate of blood glucose change for the previous hour. Themonitor can then determine a prediction of the “morning glucose” levelat wake up based upon the calculated average blood glucose and the rateof blood glucose change. In one embodiment the “morning glucose” ispredicted assuming that the rate of change remains constant, however inother embodiments nonlinear characteristic curves and functions can beapplied in making the prediction. If the anticipated “morning glucose”level is greater than a high threshold value (e.g., but not limited to,126 mg/dL), or less than a low threshold value (e.g., but not limitedto, 60 mg/dL), an alarm is sounded. This will allow time for theinfusion device basal rate to be adjusted appropriately. In alternativeembodiments, different times before anticipated wakeup, different highthreshold values, or different low threshold values, may be used.

In some embodiments, the triggering criteria can also be parameterizedto allow the user to customize the values. In some embodiments, the useris allowed to set the values for the controlling parameters. Forexample, the user can set the qualifying low and high glucose levels aswell as the anticipated waking time. For each of the settings a defaultvalue can be used in the absence of a user setting. For example, adefault low glucose level of 60 mg/dL, a default high glucose level of126 mg/dL and an anticipated waking time of 7:00 AM can be used. Inaddition, the entire function can be enabled and disabled.

FIG. 3B is a flowchart of a method for detecting an inadequate nocturnalbasal rate 320. At block 322, the method begins by measuring acharacteristic level to obtain a measurement value. The value isrecorded at block 324. Measuring and recording is repeated periodicallyto obtain a series of values at block 326. At block 328, the average ofthe series of values is calculated. At block 330, a slope of a line fitto the series of values is calculated. The calculated slope and averageof the series of values are then used to determine a predictive curve atblock 332. At block 334, the curve is extrapolated to predict a glucoselevel at wakeup. Those skilled in the art understand that suchcalculations are not limited to slope y=mx+b, and that, in this context,one can use alternative filtered arrangements as are known in the art.The extrapolation is performed some time before wakeup (e.g., but notlimited to, 3 hours prior) to provide enough time to correct anyimpending negative condition. The predicted glucose level is compared toan acceptable range at block 336. If the predicted glucose value fallswithin the range, the process ends. If the predicted glucose value fallsoutside the range, a morning glucose incident is reported at block 338.

C. Monitor for Anticipating Hyperglycemic Incidents

In another embodiment of the invention, a glucose monitor anticipates ahyperglycemic (or hypoglycemic) incident by monitoring trends in glucoselevels. The monitor alerts the patient when a “relatively steadyincrease” (or decrease) in glucose levels occurs. The monitorperiodically measures glucose, analyzes the present trend, determineswhether a hyperglycemic (or hypoglycemic) incident is probable andappropriately alerts the patient.

In one embodiment, the device measures glucose values at a specific timeinterval (e.g. once every minute), and then, e.g. at 5 minute intervals,applies a smoothing filter to this group of values and records thefiltered value. If the most recent (filtered) value exceeds a thresholdvalue (e.g., but not limited to, 180 mg/dL), the monitor calculates theslope of a line fit to a recent series of recorded values (for example,but not limited to, six values). If the slope is greater than athreshold rate (e.g., but not limited to, 3% per minute), ahyperglycemic incident is likely and the monitor alerts the patient. Forhypoglycemic incidents, values and thresholds corresponding to lowglucose levels would be used.

The threshold value is applied in a similar manner to the “qualifyingrange” applied in determining a glucose crash previously discussed. Thethreshold value effectively operates as an open range (e.g., but notlimited to, greater than 180 mg/dL). In other embodiments, the thresholdvalue can be a closed range. Therefore, determining a hyperglycemicincident can be unconcerned with values below the threshold value (asdetermining a hypoglycemic incident can be unconcerned with values abovea threshold value). In one embodiment, a slope calculation can beavoided if the current reading is outside the range. However, inalternate embodiments, the slope can be calculated and compared to thethreshold rate with every new reading. In further embodiments, multiplequalifying ranges and threshold rates can be applied to evaluate theglucose dynamics and determine triggering a hyperglycemic (orhypoglycemic) incident warning.

Here again, in some embodiments the criteria can be parameterized toallow the user to customize the controlling values for anticipatinghyperglycemic (or hypoglycemic) incidents. For example, some embodimentscan allow the user to set the glucose threshold level and/or thethreshold rate. Embodiments of the invention can also use defaultparameters if no user settings are provided (e.g., but not limited to, athreshold level of 180 mg/dL and a maximal rate of 3% per minute).Embodiments of the invention can also enable and disable this function.

FIG. 3C is a flowchart of a method for anticipating a hyperglycemicincident 350. The method begins at block 352 by repeatedly measuring acharacteristic level to obtain a group of values. At block 354, asmoothing filter is applied to the group of values to obtain a filteredmeasurement value. The filtered value is recorded at block 356. Therecorded value is compared to a threshold value at block 358. If therecorded value does not exceed the threshold value (e.g., but notlimited to, 180 mg/dL), the process returns to block 352. If therecorded value does exceed the threshold value, a slope of a line fit toa recent series of values is calculated at block 354. The calculatedslope is compared to a threshold rate (e.g., but not limited to, +3% perminute) at block 362. If the slope is not steeper than the thresholdrate, the process returns to block 352. If the slope is steeper than thethreshold rate, an anticipated hyperglycemic incident is reported atblock 364. For hypoglycemic incidents, corresponding steps for lowglucose levels would be used. As noted previously, estimates of dG/dtmay be calculated by a variety of methods known in the art including theslope (and that such calculations are not limited to, for example,determinations based on y=mx+b).

D. Monitor for Maximizing Athletic Performance

Dynamic monitoring can also be used to provide feedback based upon theengaged activity of the user. For example, the monitor can be used tomaximize performance during an endurance type activity (e.g., but notlimited to, a marathon race). The endurance athlete strives to burnglucose rather than fat and accordingly needs to anticipate low glucoselevels and ingest carbohydrates early enough to avoid low glucoselevels.

In such embodiments, the monitor anticipates low glucose levels andalerts the athlete to ingest carbohydrates. It is important to note thatthis embodiment is not strictly anticipating hypoglycemic incidents.Instead it is anticipating low glucose levels where it would otherwisebe too late for the athlete to compensate by ingesting carbohydrates andstill perform effectively and/or at full capacity.

In one embodiment, once a minute, the device measures a glucose level,applies a smoothing filter and records the filtered value at 5-minuteintervals. If the most recent recorded (i.e., filtered) value is in aqualifying range (e.g., but not limited to, 60-140 mg/dL), the processorcalculates the slope of a line fit to the most recent six filteredvalues and determines if the slope is steeper than −1% (i.e., but notlimited to, 30 mg/dL in 30 minutes). If the rate of decline exceeds thisthreshold, a low glucose level is likely and the monitor alerts theathlete accordingly. Thus, for example, but not limited to, to triggeran alarm, the glucose level rate, dG/dT, is negative with a magnitudegreater than 1% per minute for 30 minutes beginning in range 60-140mg/dL.

Similar to the glucose crash monitor, in embodiments for maximizingathletic performance the qualifying range can be a closed range (e.g.,but not limited to, between 60 and 140 mg/dL) or an open range (e.g.,but not limited to, less than 140 mg/dL). By first identifying whether amost recent value is within the qualifying range, further calculation ofthe dynamic behavior of the physiologic characteristic is avoided.Although, other alarms which merely monitor the current characteristicvalue can be triggered when the reading is too high or too low. However,in alternate embodiments, the slope can be calculated and compared tothe threshold rate with every new value. In further embodiments,multiple qualifying ranges and threshold rates can be applied toevaluate the glucose dynamics and determine triggering a low glucosewarning.

Here too, these criteria can be parameterized to allow the user tocustomize the values. Typically, the monitor will allow a user to setthe qualifying glucose range and/or enable and disable the function. Adefault qualifying range (e.g., but not limited to, 60-140 mg/dL) can beused.

FIG. 3D is a flowchart of a method for maximizing athletic performance370. The process begins at block 372, where a characteristic level isrepeatedly measured to obtain a group of characteristic level values.Following this at block 374, a smoothing filter can be applied to thegroup of characteristic level values to produce a filtered measurementvalue. The filtered measurement value is recorded at block 376. At block378 it is determined if the recorded value falls within a qualifyingrange (e.g., but not limited to, between 60 to 140 mg/dL). If not, theprocess returns to block 372. If the recorded measurement is within therange, a slope of a line fitted to a recent series of recorded filteredvalues is calculated at block 380. The calculated slope is compared to athreshold rate (e.g., but not limited to, −1% per minute) at block 382.If the calculated slope is not steeper than the threshold rate theprocess returns to block 372. If the slope exceeds the threshold rate,an anticipated low glucose level is indicated at block 384. As notedpreviously, estimates of dG/dt may be calculated by slope as well asother methods known in the art

4. Multiple Glucose Alarm Function

Embodiments of the invention can also employ multiple alarms that can beindependently set by the user. For example, a continuous glucosemonitoring system can have multiple alarms for different glucose values.The system can allow a user to set threshold glucose values that definea “narrow” glucose range (as compared to the ordinary alarm limits). Ifthe user's glucose level passes outside the “narrow” range, an alarm cansound. This alarm alerts the user to monitor his glucose levels moreclosely. The system can sound a second alarm (preferably having a sounddistinguishable from the first “narrow” range alarm) in the even theuser's glucose level reaches a more dangerous condition requiringimmediate action. Alarm indications may be audible, tactile, vibratory,visual, combinations of alarm indications, or the like. In the case ofvisual alarm indications, but not limited to, green lights can bedisplayed for with a range; yellow for the first alarm level; and redfor the second alarm level. The visual alarm indications may flashand/or also be combined with other alarm indications.

Although the above example describes a two-layer alarm system, furtherembodiments of the invention can incorporate multiple alarm layers. Inaddition, the alarms can be set in ranges or separate high and lowglucose level alarms can be set. Distinctive sounds can be used for eachalarm. For example, each successive high glucose level alarm can have,but is not limited to having, a higher pitch. Successive low glucoselevel alarms can each have, but are not limited to having, loweringpitches. Alternately, intermittent or wavering volumes that alsoincrease in pitch according to the severity of the condition can beused. In still other embodiments, the user can select or program alarmtones and other sounds and assign them to the various alarms. Also, insome embodiments, these distinguishable alarms can also be set atdifferent volume levels. In addition, as discussed above, the alarms arenot limited to audible signals; some embodiments of the invention canalso utilize visual alarms, such as flashing lights or displays ortactile alarms, such as vibrating indicators.

In still further embodiments, threshold values and associated alarms canbe set according to a schedule. For example, but not limited to,particular alarms can be set to be active only during selected portionsof the day.

FIG. 4 illustrates a multiple alarm function of the invention. A plot ofthe monitored characteristic value 400 (e.g., blood glucose) changingover time is shown. A typical wide alarm range 402 is defined by anupper threshold value 404 and a lower threshold value 406. If themonitored characteristic value 400 should exceed the defined range andcross either threshold, an alarm is initiated to indicate to the user tocheck his blood glucose. In one embodiment, a distinctive alarm can beassociated with the alarm range 402. Thus, the same alarm is producedwhether the range 402 is exceeded by passing the upper threshold value404 or the lower threshold value 406. In other embodiments, distinctivealarms can be assigned to each threshold value 404, 406. In furtherembodiments of the invention, other alarm ranges can also be set. Forexample, a second narrower range 408 can be set with a lower upperthreshold value 410 than that of the wider range 402; and a higher lowerthreshold value 412 than that of the wider range 402. As with the widerrange 402, an alarm is initiated if the narrower range is exceeded bythe monitor characteristic value 400. Here also, alarms can be the sameor different for each threshold 410, 412.

The ability to set different ranges and associated alarms allows themonitor to immediately convey some information about the condition ofthe user even before checking the actual readings. Particularly, usingthe narrower range 408 and associated alarms allows the user to know ofa negative trend that does not require the same urgency as an alarmtriggered by the wider range 402. In effect, the user is able to setmultiple alarms, each indicating a different level of urgency and/ordifferent conditions. In some embodiments, threshold values for alarmscan also be set independent from ranges.

In addition, in still further embodiments alarms or indicators can beset according to the direction in which a threshold value is crossed bythe monitored characteristic value 400. For example, as the monitoredcharacteristic value 400 crosses a lower threshold value 412 from thenarrow range (e.g., but not limited to, at point 414), one type of alarmcan be provided. However, when the monitored characteristic value 400crosses a lower threshold value 412 from the wider range 402 (e.g., butnot limited to, at point 416), another type of alarm can be provided.The difference in the alarms is appropriate because only the former caseindicates a worsening of the user's condition. In the latter case, thetransition actually indicates an improvement in the user's condition.Thus, in some embodiments of the invention, alarms will only be givenwhen crossing a threshold indicates a worsening of the user's condition.In other embodiments, an indicator will also be given when a thresholdhas been crossed in an improving direction. In these cases, either thesame indicator (sound, light, display or other) or different indicatorscan be used. In a similar manner, reminders can be set to indicate to auser various conditions (not necessarily negative) that will aid in theconvenient therapy management.

5. Advanced Blood Glucose Reminder Functions

Another aspect of the invention allows the user to set reminders thatwill be provided by the monitor. The reminders can be alarm signals(including, but not limited to, auditory, visual, tactile, etc.) thatare initiated after a timer has run to prompt the user to take action ormerely inform the user of a particular status. The reminder is started(i.e. the timer is initiated), when an event occurs and/or certainconditions are met. The alarm signals can be the same or different basedupon the triggering events or conditions. These reminders can be used tofurther assist the user in managing insulin delivery for optimumresults. For example, but not limited to, reminders can be set for eventmarkers, blood glucose values, reference values, high or low sensormeasurements.

Characteristic monitors and infusion devices can use event markers thatplace tags in the data for events the user experiences (e.g., but notlimited to, meals, exercise, and high or low blood glucose). Forexample, but not limited to, when an infusion device identifies a highor low blood glucose event marker, it can start a timer that reminds theuser to check blood glucose levels. This is intended to make therapysafer by encouraging more frequent checks during times that the patientmay be at risk from hypoglycemia or hyperglycemia. In addition, thisfeature can also be applied to characteristic monitors. For example, butnot limited to, a characteristic monitor that is used to show low orhigh blood glucose tags can have a timer set to remind a user to checktheir blood glucose levels at a later time.

In addition, a reminder timer can be set that is triggered if a bloodglucose value is entered. For example, but not limited to, the remindercan be if the user enters a low or high blood glucose value into themonitor as a reference or calibration value.

A reminder timer can also be triggered by a user providing a referencevalue to the monitor. Thus, the user can be reminded to supply a newreference value after a minimum time period has elapsed. In this waycalibration of the monitor is assured.

A blood glucose reminder can also be triggered by high or lowmeasurement from the sensor. Thus, the monitor will request a bloodglucose reference value during an excursion away from the normal rangeof values. The trigger for this reminder can be tempered by setting aminimum time between reminders to avoid pestering the user. Thisreminder can be used to provide more robust data for curve fitting ascorrelation improves with variability in the data pairs. The reminderpromotes more frequent data collection during more critical periods(e.g., but not limited to, when blood glucose is too high or too low)and therefore the interpolated curve for this period is more reliablyrepresentative of the true curve.

One aspect behind the use of these reminders is that they also serve toprevent redundant and excessive alarms for the user. For example, if thetimer is removed from the previously described high or low measurementreminder, the result would be a simple hypoglycemia or hyperglycemiaalarm. Using a reminder, however, the message is not that the user'sblood glucose is out of range. Rather, the reminder's message is tocheck the user's blood glucose with a meter, or the like. If a user'sblood glucose is very near an alarm triggering threshold, an alarm mightbe triggered repeatedly as the value passes back and forth across thethreshold. A reminder will set a timer, preventing duplicative warningsfor a short period of time, but reminding the user to check bloodglucose again when that period has expired. This can provide a better oreasier path through the regulatory process. Thus, reminders are lesslikely to become a nuisance to the user and also prompt more useful datacollection. In alternative embodiments, the alarm is triggered again,regardless of the presence of a time, if the glucose level continues tochange in the direction of the trend.

FIG. 5 illustrates a reminder function of the invention triggered byhigh or low characteristic values. A plot of a monitored characteristicvalue 500 (such as, but not limited to, blood glucose) is shown. One ormore ranges 502, 504 define safe characteristic values (e.g., but notlimited to, a first range 502 being a warning range and a second range504 being a critical range), such as can be employed using multiplealarms as previously described. When a range is exceeded (e.g., but notlimited to, at time 506), an alarm can be triggered but also a timer isstarted such that a reminder is also initiated after its expiration(e.g., but not limited to, at time 508). Over the timer period furtheroccurrences of exceeding the threshold (e.g., but not limited to, atpoint 510) will not result in a duplicative alarm.

However, the situation can be somewhat different when the interveningtriggering event is not identical to the first triggering event. Forexample, if a first range 502 is exceeded (e.g., but not limited to, attime 512) and a timer is started, but before a reminder can be issued(e.g., but not limited to, at time 514) a second range 504 is exceeded(e.g., but not limited to, at time 516), then the second alarm will beissued and the timer will be restarted. No reminder will be indicated atthe theoretical expiration of the first timer (e.g., but not limited to,at time 514), but a reminder will be issued at the expiration of thesecond timer (e.g., but not limited to, at time 518). In this case,exceeding the second range overrides the first reminder because thesecond alarm is a different, albeit related, condition. As previouslydescribed, however, the use of reminders is not limited to monitoringhigh and low characteristic values. In a similar manner, reminders canbe triggered by user's supplied reference values for calibration as wellas event markers entered into the monitor.

6. Glucose Monitoring Information Management

Another aspect of the invention is to provide meaningful retrospectiveinformation to the patient using the sensor. In particular, aretrospective display of one or more physiological values can providesignificantly useful data. As disclosed, the retrospective displays canbe designed in a variety of ways to provide various useful information.For example, but not limited to, as the sleeping user receives nobenefit from a real-time display, a retrospective view of data isimportant. While a simple listing of previous values has value, it canbe time consuming to review, provides information that is difficult tovisualize and comprehend and requires significant memory space withinthe device. Providing useful information that is easy to understand andthat can be stored within a small memory space is very important. Theability to review data from the previous sleep period is particularlyhelpful to a user with nocturnal hypoglycemia or “dawn effect”, as thereis typically no witness to the real-time display. These measures can beeven more important in cases where the alarm system can exhibit manyfalse positives and/or false negatives, which might otherwise frustratethe user and lead to non-use of the monitor.

The following advanced data presentation tools can be used toconveniently and efficiently store and display useful information on ascreen for a user to review while the monitor is in use. The toolsprovide useful information while requiring only a minimal amount memoryspace. These data presentation tools can also be used in anyretrospective analysis package, such as software running on a computeror network designed to analyze trends and provide advise regarding atreatment regime.

The tools operate by processing that compares actual reading to high andlow value limits (e.g., but not limited to, acceptable blood glucoseranges). For example, but not limited to, the limits can be theadjustable hypoglycemic and hyperglycemic alarm thresholds of a monitor.Alternately, for standardization, the tools can be applied to a fixeddefinition of a target blood glucose range that is independent of thehyperglycemic and hypoglycemic alarm thresholds for the particularuser/monitor.

FIG. 6A illustrates one minimum and maximum data presentation. A displayof the minimum and maximum values 600 of the characteristic monitor thathave been measured for the user can be displayed on the monitor. Theminimum value and maximum values can be conveniently displayed alongwith the date and time of their occurrence. Such a display 600 isuseful, but becomes more useful when combined with an excursion count, adistribution of values, and/or integrated values as discussed below

FIG. 6B illustrates an excursion data presentation. The number ofexcursions above or below the respective blood glucose limits is alsovery useful to have summarized for the user. An excursion display 602provides good information, particularly when there are no alarms activeon the monitor (either because the monitor is not turned on or alarmsare not being employed by the user). A display 602 of the number ofexcursions above the hyperglycemic limit and the number of excursionsbelow hypoglycemic limit give the user an idea of performance of atreatment program at a glance. A high number of incidents exceedingeither limit indicate a need for improvements.

FIG. 6C illustrates a characteristic value distribution datapresentation. A simple distribution of sensor values offers a verypowerful tool. In a preferred embodiment, the distribution is describedin percentages that are automatically scaled with the duration ofmonitor use. Optionally, a monitor can include the total time of usewith a percentage distribution. Awareness of a total time providesperspective for reviewing the percentage distribution. A time baseddistribution can also be used, but requires the total time to beincluded in the analysis as a reference. A distribution can also bepresented based upon the total number of readings, but requires thetotal time is required in the analysis.

For example, but not limited to, the display can show a percentage ofreadings above a hyperglycemic alarm level, a percentage of readingsbelow a hypoglycemic alarm level and a percentage of readings ofreadings within alarm range as shown in FIG. 6C. Optionally, the totaltime covered in the analysis can also be displayed. Similarly, analternate display can show the time spent above a hyperglycemic alarmlevel, the time spent below a hypoglycemic alarm level and the timespent within alarm range (not shown). As mentioned, the time basedisplay requires a known total time as part of the analysis. Finally, adisplay can also include the number of readings above hyperglycemicalarm level, the number of readings below a hypoglycemic alarm level andthe number of readings within alarm range (not shown).

FIG. 6D illustrates an integrated characteristic value datapresentation. Performing an integration of the readings outside thealarm levels with respect to time can provide a measure of thehypoglycemic and hyperglycemic events' severity. In addition, theseresults can also be scaled these by a total sensor time to provide ameasure that is duration independent.

For example, a “hyperglycemic area” can be calculated as the sum of thedifferences between the readings and the hyperglycemic alarm limit. A“hypoglycemic area” can be calculated from the sum of all thedifferences between the hypoglycemic alarm limit and the readings. A“hyperglycemic index” is calculated by taking the “hyperglycemic area”and dividing it by the duration of sensor use. Similarly, the“hypoglycemic index” can be calculated by taking the “hypoglycemic area”divided by the duration of sensor use.

CONCLUSION

Various alarms and/or monitoring aspects discussed above may be combinedor utilized with other alarms and/or monitoring aspects. The possibleembodiments and/or combinations should not be limited to the specificembodiments described above.

This concludes the description including the preferred embodiments ofthe present invention. The foregoing description including the preferredembodiment of the invention has been presented for the purposes ofillustration and description. It is not intended to be exhaustive or tolimit the invention to the precise form disclosed. Many equivalentmodifications and variations are possible in light of the aboveteaching.

It is intended that the scope of the invention be limited not by thisdetailed description, but rather by the claims appended hereto. Theabove specification, examples and information provide a description ofthe manufacture and use of the apparatus and method of the invention.Since many embodiments of the invention can be made without departingfrom the scope of the invention, the invention resides in the claimshereinafter appended. Throughout this application, various publicationsare referenced. The disclosures of these publications are herebyincorporated by reference herein in their entireties.

1. A physiological characteristic monitor, comprising: an input devicecapable of receiving a signal from a sensor, the signal being based on aphysiological characteristic value of a user; a processor for analyzingthe received signal; and a memory for storing data and instructions usedby the processor; wherein: the physiological characteristic is bloodglucose; the processor initiates a timer based upon a conditionassociated with the blood glucose value of the user, wherein aninitiating condition comprises hyperglycemia or hypoglycemia and aduration of the timer is preset based upon the initiating condition; andthe processor provides a reminder to the user following expiration ofthe timer, wherein the reminder: prevents an alarm from being initiatedfor a first period of time; and initiates an alarm that reminds the userto monitor blood glucose when the first period of time has expired. 2.The physiological characteristic monitor of claim 1, wherein thereminder includes an alarm signal selected from the group consisting ofan audible signal, a visual signal, a tactile signal and a display. 3.The physiological characteristic monitor of claim 1, wherein thecondition is that an event marker is entered into the monitor.
 4. Thephysiological characteristic monitor of claim 3, wherein the eventmarker is selected from the group consisting of a meal marker, anexercise marker, a high blood glucose marker and a low blood glucosemarker.
 5. The physiological characteristic monitor of claim 1, whereinthe condition is that a reference value is entered into the monitor andthe reminder indicates that a new reference value should be entered. 6.The physiological characteristic monitor of claim 1, wherein theprocessor determines a physiological characteristic value from thereceived signal and the condition based upon the physiologicalcharacteristic value.
 7. The physiological characteristic monitor ofclaim 1, wherein the condition is that the physiological characteristicvalue exceeds a threshold value.
 8. The physiological characteristicmonitor of claim 1, wherein the condition is that the physiologicalcharacteristic value is below a threshold value.
 9. The physiologicalcharacteristic monitor of claim 1, wherein the sensor is placed insubcutaneous tissue.
 10. The physiological characteristic monitor ofclaim 1, wherein the sensor is placed in interstitial fluid.
 11. Amethod of triggering a reminder to a user of a physiologicalcharacteristic monitor, comprising the steps of: receiving a signal froma sensor, the signal being based on a physiological characteristic valueof a user, wherein the physiological characteristic is blood glucose;using a processor and a memory that stores data and instructions used bythe processor to analyze the received signal and to initiate a timerbased upon a condition associated with the blood glucose value of theuser, wherein an initiating condition comprises hyperglycemia orhypoglycemia and a duration of the timer is preset based upon theinitiating condition; and using the processor to provide a reminder tothe user following expiration of the timer, wherein the reminder:prevents an alarm from being initiated for a first period of time; andinitiates an alarm that reminds the user to monitor blood glucose whenthe first period of time has expired, so as to provide a reminder to theuser following expiration of the timer.
 12. The method of claim 11,wherein the reminder includes an alarm signal selected from the groupconsisting of an audible signal, a visual signal, a tactile signal and adisplay.
 13. The method of claim 11, wherein the condition is that anevent marker is entered into the monitor.
 14. The method of claim 13,wherein the event marker is selected from the group consisting of a mealmarker, an exercise marker, a high blood glucose marker and a low bloodglucose marker.
 15. The method of claim 11, wherein the condition isthat a reference value is entered into the monitor and the reminderindicates that a new reference value should be entered.
 16. The methodof claim 11, wherein the processor determines a physiologicalcharacteristic value from the received signal and the condition basedupon the physiological characteristic value.
 17. The method of claim 11,wherein the condition is that the physiological characteristic valueexceeds a threshold value.
 18. The method of claim 11, wherein thecondition is that the physiological characteristic value is below athreshold value.
 19. The method of claim 11, wherein the processorprovides an alarm based upon the condition associated with thephysiological characteristic value of the user before initiating thetimer.
 20. A physiological characteristic monitor, comprising: an inputdevice capable of receiving a signal from a sensor placed insubcutaneous tissue, the signal being based on a blood glucose value ofa user; a processor for analyzing the received signal; and a memory forstoring data and instructions used by the processor; wherein: theprocessor initiates a timer based upon a condition associated with theblood glucose value of the user, wherein an initiating conditioncomprises hyperglycemia or hypoglycemia and a duration of the timer ispreset based upon the initiating condition; and the processor provides areminder to the user following expiration of the timer, wherein thereminder: prevents an alarm from being initiated for a first period oftime; and initiates an alarm that reminds the user to monitor bloodglucose when the first period of time has expired.
 21. The physiologicalcharacteristic monitor of claim 20, wherein: the sensor comprises anelectrode; and the electrode is exposed for direct contact with blood oranother body fluid when the sensor is subcutaneously placed at aninsertion site.
 22. A method of triggering a reminder to a user of amonitor, comprising the steps of: receiving a signal from a sensorplaced in subcutaneous tissue, the signal being based on a value of auser; using a processor and a memory that stores data and instructionsused by the processor to analyze the received signal and to initiate atimer based upon a condition associated with the value of the user,wherein an initiating condition comprises hyperglycemia or hypoglycemiaand a duration of the timer is preset based upon the initiatingcondition; and using the processor to provide a reminder to the userfollowing expiration of the timer, wherein the reminder: prevents analarm from being initiated for a first period of time; and initiates analarm that reminds the user to monitor blood glucose when the firstperiod of time has expired, so as to provide a reminder to the userfollowing expiration of the timer.
 23. The method of claim 22, wherein:the sensor comprises an electrode; and the electrode is exposed fordirect contact with blood or another body fluid, when the sensor issubcutaneously placed at an insertion site.